1. Field of the Invention
This invention relates to a picture display apparatus for magnifying a portion of a picture displayed on a screen for display on the same screen.
2. Description of the Related Art
In general, if, when displaying a picture, such as a character, figure or a photo on a display, such as a cathode ray tube (CRT), it is desired to improve decipherability of fine-textured portions of a picture, it is necessary to display a picture of the fine-textured portions to a more or less enlarged scale. Since the display area on the screen is of a limited size, a so-called scroll function of displaying the new information by sequentially feeding the new information on upper, lower, left and right portions of the display area. With this scrolling function, if scrolling is done in the downward direction, the information displayed at an uppermost portion of the display area disappears from the display area and hence ceases to be displayed.
The above-described technique has a drawback that, since the information in its entirety cannot be viewed on the display, it is not apparent at which position of the entire information the currently displayed information is located, while it is difficult to designate the picture portion desired to be viewed.
For overcoming this deficiency, the present Assignee has disclosed in JP Patent Kokai Publication JP-A-4-337873 (1992) a picture display apparatus in which two display portions, that is a display portion for displaying the entire information and a display portion for displaying a partial information to an enlarged scale, are provided on one and the same display screen.
In the picture display apparatus, disclosed in the above Publication, an overall display portion 1 for accommodating the entire information and a magnified display portion 2 are provided on the display screen, as shown in FIG. 1. The magnified display portion 2 is designed for displaying the contents of a rectangular display portion 5 pointed by a cursor 4 in the overall display portion 1 to an enlarged scale. In U.S Pat. No.4,751,507, FIG. 5, there is similarly disclosed a technique of displaying an overall picture 1 and a partial magnified picture designated by the cursor in separate regions of one and the same screen.
However, if a portion of the entire picture is displayed to an enlarged scale as described above, since the information display portion is divided into the overall display portion 1 and the enlarged display portion, the viewer (user of the display apparatus) has to move his or her line of sight frequently in order to view these two portions simultaneously. This leads to fatigued feeling or mistaken recognition. The two display regions, that is the overall display region 1 and the enlarged display region take up a larger portion of the display area on the screen. If rectangular regions are allocated to the overall display region 1 and the magnified display region 2, there is produced on the screen a region 3 not used for display thus obstructing efficient utilization of the display screen. These defects of the apparatus of the above referenced Publications cancel the merits that the relative position of the magnified picture portion in the overall picture can be comprehended easily and the picture portion desired to be viewed to an enlarged scale can be designated easily.
Although it is envisaged to display the magnified display region in superimposition on the overall display region, since the magnified display region is selected by area designation using a cursor displayed on the overall display region and a magnified display region corresponding to the selected display area is displayed in superposition on the overall display region, it becomes difficult to select further a picture portion hidden by the magnified display region. If the picture potion hidden by the enlarged display region is selected and newly displayed to an enlarged scale, it becomes necessary to perform a complex operation of moving the existing magnified display region to a different place or erasing the magnified display region and selecting a region to be displayed next to an enlarged scale for displaying the newly selected region in the new magnified display region.